linux-kernel - Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO

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Message-ID: <2402062b-aae6-a247-06a8-3775c2909bdb@gmail.com>
Date:   Wed, 29 Jun 2022 12:14:42 +1200
From:   Michael Schmitz <schmitzmic@...il.com>
To:     Bart Van Assche <bvanassche@....org>,
        Arnd Bergmann <arnd@...nel.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        scsi <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jakub Kicinski <kuba@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        Khalid Aziz <khalid@...ehiking.org>,
        "Maciej W . Rozycki" <macro@...am.me.uk>,
        Matt Wang <wwentao@...are.com>,
        Miquel van Smoorenburg <mikevs@...all.net>,
        Mark Salyzyn <salyzyn@...roid.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        alpha <linux-alpha@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        Denis Efremov <efremov@...ux.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Subject: Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS

Hi Bart,

On 29/06/22 12:01, Michael Schmitz wrote:
>
>> An example of a user space application that passes an SG I/O data 
>> buffer to the kernel that is aligned to a four byte boundary but not 
>> to an eight byte boundary if the -s (scattered) command line option 
>> is used: 
>> https://github.com/osandov/blktests/blob/master/src/discontiguous-io.cpp
>
> Thanks - four byte alignment actually wouldn't be an issue for me. 
> It's two byte or smaller that would trip up the SCSI DMA.
>
> While I'm sure such an even more pathological test case could be 
> written, I was rather worried about st.c and sr.c input ...
Nevermind - I just see m68k defines ARCH_DMA_MINALIGN to be four bytes. 
Should be safe for all that matters, then.

Cheers,

     Michael